Goussia Labbe´ , 1896 (Apicomplexa, Eimeriorina) - Institute of ...

132 M. Jirku˚ et al.
output, necessarily lead to contamination of the
aquatic environment, with oocysts being immediately
infectious for new hosts due to their
endogenous sporulation. In general, the tadpoles
of anuran species involved in this study often
occur syntopically, and it is unlikely that receptive
hosts could remain uninfected in such conditions
if the host range of Goussia found involved hosts
from different genera. While the anuran Goussia
isolates cannot be distinguished from each other
and from G. neglecta by oocyst/sporocyst morphology,
the 3—4% divergence of their SSU rDNA
sequences indicates that each anuran genus
hosts a distinct Goussia species. Infection experiments
suggest that the closely related R. dalmatina
and R. temporaria (Veith et al. 2003) are
parasitized by G. noelleri. The most plausible
explanation for the peculiar pattern of distribution
in different localities, absence of morphological
differences and sequence divergence among the
anuran isolates is that three cryptic Goussia spp.
parasitize Rana spp., P. kl. esculentus and B. bufo,
respectively. This conclusion conforms with Molnár
et al. (2005), who showed that morphologically
indistinguishable Goussia carpelli isolates from
different cyprinid fish represent distinct species
with a narrow host specificity.
Interestingly, post mortem examination showed
that the coprological results obtained by flotation
do not reflect the real prevalence of Goussia
in tapoles, possibly as a result of intermittent
oocyst shedding, rendering coprology unsuitable
for prevalence assessment of Goussia species.
In agreement with others (Paperna et al. 1997)
we found that Goussia infections are common
among anuran tadpoles. Given their narrow host
specificity, the diversity of anuran Goussia might
thus be remarkable. However, the morphology
of oocysts/sporocysts as well as their size
ranges overlap in known anuran Goussia spp.
and should not be considered a primary taxonomic
criterion.
While oocysts/sporocysts of anuran Goussia
are morphologically rather uniform, possibly as a
consequence of being subject to similar selection
forces, the situation may be different for the
endogenous stages, which develop in the digestive
tract of tadpoles. Different physiological environments
of their hosts might therefore represent major
selection mechanisms leading to species-specific
morphological adaptations. Information on endogenous
development should thus become regular
part of future studies, that should incluce also
molecular data. Following the proposed taxonomic
requirements, we consider differences in the SSU
ARTICLE IN PRESS
rDNA sequence of the B. bufo isolate insufficient for
the description of a new species.
Differential Diagnosis of G. noelleri
At the ultrastructural level, G. noelleri is characterized
by the absence of wall-forming bodies and
parasitophorous vacuole in the gamogonic and
sporogonic stages, presence of pellicular projections
in macrogamonts, two refractile bodies per
sporozoite, each surrounded by fine amylopectin
granules, an unilayered sporocyst wall without
transverse striation and a simple sporocyst suture.
The lack of wall-forming bodies is a common trait
of fish and amphibian coccidia (Paperna and
Lainson 1995; Paperna et al. 1997), while the
absence of a parasitophorous vacuole seems to
be specific for G. noelleri. Another feature differentiating
the anuran G. hyperolisi and G. noelleri
from most piscine congeners is the absence of the
sporocyst wall striation (Lom and Dyková 1992).
Refractile bodies were observed in G. hyperolisi,
yet in contrast to G. noelleri, no amylopectin
granules were observed on their surface (Paperna
et al. 1997). However, a layer of amylopectin
granules reminiscent of that observed around
refractile bodies of G. noelleri was described from
anuran Eimeria bufomarini and piscine Goussia
sinensis (Baska and Molnár 1989; Paperna and
Lainson 1995).
Status of the genus Goussia: The solitary position
of G. janae at the base of the eimeriorinid
coccidia, along with the branching of the anuran
Goussia spp. and the piscine G. metchnikovi
within the Eimeriidae s.l. clade suggest that the
genus Goussia is paraphyletic, characterized by
non-unique features such as four bivalved dizoic
sporocysts per oocyst. Moreover, this feature
is shared with the reptile-host coccidian genera
Acroeimeria and Choleoeimeria (Paperna and
Landsberg 1989). Importantly, the polytomy of
the anuran Goussia spp. and G. metchnikovi
shows that basal eimeriid lineages are undersampled
and taxonomic rearrangements using the
limited available dataset would be unstable.
As there are two poorly characterized type
species of the genus Goussia (Levine 1983),
topotypic material is needed to redefine them,
and re-evaluate the taxonomy of the Goussia-like
piscine and amphibian coccidia. The genus
should be redescribed by combination of oocyst/
sporocyst morphological features, character of
the endogenous development and phylogenetic
affinity of the type species. Paperna and Landsberg
(1989) erected the genera Acroeimeria and